The present invention concerns a balun, consisting of four coupled planar lines running next to each other, with an unbalanced connection gate and two balanced connection gates.
Baluns are known to be transitions between balanced and unbalanced transmission lines. A balanced line exists when a signal being transmitted over it does not have ground as reference potential. On the other hand, an unbalanced transmission line is connected on one side to ground, so that a signal being transmitted over it has ground as reference potential. Baluns of this type are used, for example, at the inputs and outputs of quadruplex mixers or amplifiers or modulators, etc.
The balun just mentioned, consisting of four planar lines connected to each other, is known from DE 197 29 761 A1. This balun consists of two 3 dB couplers, each of which consist of two planar lines coupled over a length of xcex/4. Each of the two couplers is designed in the form of a two-pole band pass filter, in which one is configured in an open circuit configuration and the other in a short circuit configuration. The two quarter-wavelength couplers are connected to each other so that a three-gate balun is produced, having one connection for unbalanced signals and two connections for balanced signals. The opposite ends of the two lines in the line coupler in the open circuit configuration are at no-load. Another end of the two lines serves as balanced connection. The opposite end of the other line is connected to one end of one of the two line couplers designed in the short circuit configuration. Two opposite ends of the two lines are contacted with ground from this line coupler, and another end of a line forms an additional connection for balanced signals. The two line ends of the two line couplers connected to each other form the connection gate for unbalanced signals. In order to achieve a narrow 3 dB coupling between the lines, the balun is designed in multilayer technology. The manufacturing cost is therefore high, which is unfavorable for mass production.
The underlying task of the invention is to provide a space-saving balun that is as simple as possible to manufacture.
This type of balun is constructed as follows according to the features of claim 1. One end of a first of four lines serves as a first balanced connection gate. The other end of this first line is connected to the end of the second line adjacent to it. The end of the second line connected to the first line forms the unbalanced connection gate, and the other end of the second line lies at ground potential. The end of the third line lying next to the unbalanced connection gate adjacent to the second line is contacted with ground, and the other end of the third line serves as second balanced connection gate. The end of the fourth line lying next to the second balanced connection gate adjacent to the third line is contacted with ground, and the other end of the fourth line is connected to the end of the second line forming the unbalanced connection gate.
According to a subclaim, the coupling length of the four lines corresponds to roughly one-fourth the average operating wavelength of the balun.